Solid state controller

ABSTRACT

A solid state circuit for slow turn on and turn off of power to a load to limit surges and transients normally associated with the switching of large loads. A thyristor and a switching unit for turning the thyristor on and off, with a phase shift network in the switching unit for turn on time control. A radiation sensitive resistor in the phase shift network illuminated by a source in turn energized by a porportional control circuit having a time delay for build-up and decay of illumination. A two-step delay circuit, and a circuit suitable for single phase and three phase systems.

United States Patent 1 [111 3,754,177

OReilly Aug. 21, 1973 [5 1 SOLID STATE CONTROLLER 3,694,692 9/1972Pressman 315/156 Inventor: Royal V. OReilly, Long Beach,

Calif.

Assignee: Lectron Corporation, Carson,

Calif.

Filed: Sept. 5, 1972 Appl. No.: 286,412

References Cited UNITED STATES PATENTS 11/1968 Miller et a1.

1/1969 Keller 9/1970 Nuckolls 5/1972 250/209 X Pfeffer 318/313 X PrimaryExaminer-B. Dobeck Attorney-Ford W. Ham's, Jr., Wolton Eugene Tinsley etal.

[5 7 ABSTRACT A solid state circuit for slow turn on and turn off ofpower to a load to limit surges and transients normally associated withthe switching of large loads. A thyristor and a switching unit forturning the thyristor on and off, with a phase shift network in theswitching unit for turn on time control. A radiation sensitive resistorin the phase shift network illuminated by a source in turn energized bya porportional control circuit having a time delay for build-up anddecay of illumination. A twostep delay circuit, and a circuit suitablefor single phase and three phase systems.

12 Claims, 3 Drawing Figures SOLID STATE CONTROLLER This inventionrelates to starting or turning on power to electrical loads,particularly larger loads which have high inrush currents when directlyconnected to the line. The current practice in motor starting andtungsten lamp turn on is to directly connect the load to the currentbecause of the low resistance of the cold filaments at switch closure.Typically the lamp transients will exist for a few cycles of a 60 cycleper second source.

Whether the high starting current condition lasts for a'few cycles aswith a pure resistive lamp load, .or a minute or more as with a largeelectric motor, or an intermediate period as with a transformer load, itis desirable to effect slow turn on or buildup of current, and also inmany instances, slow turn off or decay of current.

Current control is achieved with thyristors, such as four layer diodes,silicon controlled rectifiers and triacs. However, instantaneousswitching of thyristors under'high current conditions often results inexcessive heating and other damage to the device.

Accordingly it is an object of the present invention to provide a newand improved circuit for controlling buildup of current to an electricalload, which circuit is particularlysuitable for use with larger loadssuch as one kw, three horsepower and greater. A further object is toprovide such a circuit which controls the current buildup at turn on andcurrent decay at turn off to effectivelyproduceslow turn on and slowturn off, elimi-' low voltage, "low-power time delay section and a highvoltage, high power output section. A further object is to provide sucha circuit incorporating an RC time delay circuit, the time constant ofwhich may be selected to provide'any desired'length of time for the turnon and turn off operations.

his a further object of the invention to provide in such-a circuit. atwo-step delay wherein current buildup toa firstlevelmay be accomplishedin a first controlled periodof time and fur ther current buildup to-thesteady state condition is accomplished in a second period of time.Another object is to provide such-a circuit which maybe used withsinglephase and three phase systems. One additional object is'to providea newand'improved radiation coupler particularly suited for multiplesingle phase, two-phase and three phase systems.

Other'objects, advantages, features and results will more fully appearin the course of the following. description where thedrawing merelyshowsand the description merely describes preferred embodiments of thepresent invention which are given by way of illustration or example.

In the drawing:

FIG. 1 is an electrical schematic of a circuit incorporating thepresently preferred embodiment of the invention for a starter for athree phase motor;

FIG. 2 is a top view of a three phase radiation coupler for use with thecircuit of FIG. 1; and

FIG. is a top view of the coupler of FIG. 2.

The circuitof FIG. 1 includes a power supply 10, a lamp circuit 11, andthree thyristors 12, 13, 14 and for the three phases A, B, C,respectively, with a switching circuit 15 for each thyristor.

The power supply 10 may be conventional and provides a regulated dc.voltage at 20 for the lamp circuit 1 1. Typically the power supply mayinclude a stepdown transformer 21 with the primary connected to lineterminals 22, 23 via an on-off switch 24. The transformer secondary isconnected to a full wave rectifier 25 with a series resistor 26 and ashunt capacitor 27 in the filter circuit and with a zener diode 28 toprovide voltage regulation. An on-off switch 29 may be connected at thesecondary for remote, low voltage operation if desired.

The lamp circuit 11 includes radiation sources 30, 31, which typicallymay be incandescent lamps, but which may alternatively be light emittingdiodes or other radiation sources as desired. A transistor 32 isconnected in circuit with the lamp 30 and a resistor 33. Anothertransistor 34 is connected in series with a resistor 35 and to the baseof the transistor 32. A resistor 37 is connected in series with acapacitor 38 and another resistor 39 across the voltage source, with thejunction of resistor 37,and capacitor 38 connected to the base oftransistor 34. A transistor 40 is connected in series with the lamp 31and another resistor 41. A resistor 42 is connected in series with acapacitor 43 across the voltage source, with the junction of theresistor and capacitor connected to the base of the transistor 40. Aresistor 44 is connected between the junction of the lamp 31 andtransistor 40 and the junction of the capacitor 38 and resistor 39.

When switch 24 is closed, the capacitor 43 is charged through theresistor 42 from the output of the power supply appearing at 20. Thecurrent in the lamp 31 is controlled by the transistor 40, with thecurrent increasing as the voltage at the base of the transistor 40,corresponding to the charge on the capacitor 43, increases. I-Ience therate of increase of output of lamp 31 isa function of the time constantof the resistancecapacitance circuit 42, 43, which may be selected togive the desired delay. The intensity of the lamp'output isa function ofthe lamp itself, the power supply voltage and the circuit components,and may be selected for the particular application.

In a similar manner, the capacitor 38 is charged from the dc supplythrough resistors 37, 39 to control the current in the transistor 34which in turn controls the current in the transistor 32 and the lamp 30.The resistor 44 in combination with resistor 39 provides d.c. pedestalsuch that lamp 30 begins to turn on just after lamp 31 approachesmaximum allowable brightness. The transistor 34 supplies added isolationso that the charging time of capacitor 38 through resistor-37 is notaffected by the loading impedance of transistor 32. The rate of increaseof output of the lamp 30 is a function of the time constant of theresistance-capacitance circuit 37, 38, 39, and the intensity of the lampoutput is determined as with the lamp 31.

The preferred lamp circuit shown in FIG. 1 provides a two step delay inpower turn on as will be described. If only a single delay is desired,one of the lamps and associated circuitry may be omitted. Typically inthe two step delay configuration, the delay for one lamp is quitedifferent from that for the other, and in the embodiment illustrated forcontrol of an induction motor, the delay for the lamp 31 is in the orderof a few cycles and in the delay in the lamp 30 is in the order ofthirty seconds.

The lamp circuit 11 is a low voltage, low power circuit which iselectrically isolated from the three phase line, the controlledrectifiers and the load. Any type of switching which provides a voltageat may be utilized in lieu of the simple on-off switch 24, and the lowvoltage, low power lamp circuit is particularly suited for remoteswitching control.

The circuits for each of the thyristors 12, 13, 14 are the same, and onewill be described. The thyristor 13 is connected. between the line andload and may be any suitable thyristor and a triac is illustrated. Aresistor 50 and a capacitor 51 are connected in parallel with the triac13 for transient suppression. The switching unit 15 includes a phaseshift network 53 and a trigger unit 54. The phase shift network includesa light sensitive resistor 55, typically a conventional photocell, inseries with a capacitor 56. Also, a series circuit comprising a resistor57, another light sensitive resistor 58 and a variable resistor 59 isconnected in parallel with the resistor 55. Device 60 comprises twozener diodes, connected back to back, to establish a stable a.c.reference for network 53, such that fluctuations in line voltage willnot adversely affect the timing. I

The trigger unit 54 is connected between the phase shift network 53 andthe control element of the triac l3 and provides a triggering pulse forturning the triac on or switching the triac into conduction. A unit 54may be a conventional diac or similar component which can provide atriggering pulse in each cycle, depending upon the condition of thephase shift network. Alternatively, the unit 54 may be a conventionalunit which provides a triggering pulse only at a zero crossing of theac. supply with control being achieved by varying the number of oncycles and off cycles per unit of time, as a function of the conditionof the phase shift network.

The photocells 55 of the three switching units are disposed to receiveradiation from the lamp 30, and the photocells 58 are positioned toreceive radiation from the lamp 31. A preferred configuration for lampand photocell mounting is shown in FIGS. 2 and 3. A cubicle container 65is provided with a cover 66, with the lamp 30 mounted in the cover andprojecting into the container, to position the lamp filament at thecenter of the container. The three photocells are mounted in the centersof three faces of the container, thereby positioning the photocellsequidistant from the lamp. This container design provides a closedcoupling between the lamp and photocells, with provision for equalradiation to each photocell from the centrally disposed lamp.

Photocells normally have a maximum resistance with no incidentradiation, with the resistance decreasing to a minimum value as theincident radiation increases. Values for the components of the phaseshift network are selected so that with no incident radiation on eitherphotocell, the rectifier will not be turned on. When the lamp 31 isenergized, radiation therefrom decreases the resistance of thephotocells 58, changing the phase shift in the network 53 and providinga trigger pulse to turn on the rectifier. Similarly, when the lamp 30 isenergized, the resistance of the photocells 55 is decreased providingrectifier turn on. The turn on time can be selected as desired byselecting the values for the various components in the circuit. in theparticular embodiment illustrated, a resistance change from maximum tominimum of the photocell 58 produced in a few cycles by the currentbuildup in the lamp 31 will shift the phase of the network sufficientlyto trigger the rectifier into conduction at a predetermined andadjustable phase angle of each half cycle. The change in resistance ofthe photocell 55 from maximum to minimum which occurs in approximatelyone minute during the increase in output from the lamp 30 will furtherchange the phase in the network to maintain the triac in fullconduction. The circuit operates in the same manner when the switch 24is moved to the off or open condition, with the capacitors 38 and 43discharging and providing corresponding delays in lamp output and triacconduction time. Where only a one step delay is utilized, with the lamp31 omitted, the photocells 58 are omitted from the phase shift network.

One limiting factor in the use of thyristors is the operatingtemperature, with the heating due to internal resistance and the highcurrent load. The present circuit permits operation of two thyristors inparallel providing twice the current rating with one-half the voltagedrop. Problems normally encountered in operating two thyristors inparallel due to slight differences in turn on characteristics with aresultant full load on one thyristor, are avoided with the slow turn onfeature provided by the present circuit. Some obvious advantages areachieved with the present circuit, including elimination of movingcontacts found in conventional motor starters and the elimination ofarcing which occurs when contacts are opened under load. Otheradvantages include infinite operating life, many times the cycling life,optimum design for hazardous environment (no arcing), functions equallywell under water and at extreme altitudes and temperature ranges. Asindicated previously, the circuit is suitable for use with resistiveloads and with inductive loads. The circuit is especially adapted forconnecting a large motor to a line where the load of the motor will puta significant load on the generator supplying the electric power. Thetime delay produced by the present circuit can be matched to thereaction time of the generator in responding to the additional load sothat the generator picks up the gradually increased load without surgecurrents, transients or reduction in line voltage. Similarly, when thecircuit is used for turning on power to a large lamp load, the delay inturn on can be matched to the increase in resis tance of the lamps sothat there is substantially no inrush current or electrical impact onthe lamp filament.

I claim:

1. In a circuit for controlling buildup of power to a load, thecombination of:

a thyristor for connection in circuit between line and load, saidthyristor having a control element;

a switching unit connected to said control element for turning saidthyristor on and including a phase shift network for varying the time ofthyristor turn on,

said network including a first resistor having a resistance varying as afunction of received radiation;

a first radiation source connected in circuit with a first currentcontrol unit, with radiation from said first source directed to saidfirst resistor;

a first RC delay circuit for said first current control unit forincreasing current through said current control unit to said firstradiation source;

a voltage source; and

means for connecting said voltage source across said first delay circuitfor charging the capacitance thereof, with the current to said firstradiation source increasing as said capacitance charges to increase theon time of said thyristor.

2. A circuit as defined in claim 1 wherein said current control unitincludes a transistor with emitter and collector in series with saidfirst radiation source, with said first delay circuit connected to thetransistor base for controlling current in said first radiation source.

3. A circuit as defined in claim 1 wherein said thyristor is a triac.

4. A circuit as defined in claim 1 wherein said controlled rectifiercomprises two thyristors connected in parallel.

5. A circuit as defined in claim 1 for operation with a three phasesystem and including three of said thyristors and switching units, withradiation from said first radiation source directed to the firstresistors of each of the three switching unit networks.

6. A circuit as defined in claim 5 including a closed container, withthe first resistors of each of the three phase shift networks mounted inthe walls of said container, and with said first radiation sourcemounted within said container spaced substantially equally from each ofthe first resistors.

7. A circuit as defined in claim 6 wherein said container has a squarecross section with four faces, with said first resistors mounted inthree of said faces.

8. A circuit as defined in claim 1 including:

a second resistor in said phase shift network and having a resistancevarying as a function of received radiation;

a second radiation source connected in circuit with a second currentcontrol unit, with radiation from said second source directed to saidsecond resistor;

a second RC delay circuit for said second current control unit forincreasing current through said unit to said second radiation source;and

means for connecting said voltage source across said second delaycircuit for charging the capacitance thereof, with the current to saidsecond radiation source increasing as said capacitance charges toincrease the on time of said thyristor.

9. A circuit as defined in claim 8 with said phase shift networkconnected across said thyristor and with said first and second resistorsconnected in parallel.

10. A circuit as defined in claim 8 including means connecting saidsecond current control unit to said first delay circuit.

11. A circuit as defined in claim 10 wherein said second current controlunit and radiation source and said second phase shift network includingsaid second resistor are selected such that fully charging thecapacitance of said second delay circuit turns said thyristor on onlyfor a portion of the available on time.

12. A circuit as defined in claim 8 wherein said second current controlunit and radiation source and said second phase shift network includingsaid second resistor are selected such that fully charging thecapacitance of said second delay circuit turns said thyristor on at apredetermined and adjustable phase angle of each half cycle.

1. In a circuit for controlling buildup of power to a load, thecombination of: a thyristor for connection in circuit between line andload, said thyristor having a control element; a switching unitconnected to said control element for turning said thyristor on andincluding a phase shift network for varying the time of thyristor turnon, said network including a first resistor having a resistance varyingas a function of received radiation; a first radiation source connectedin circuit with a first current control unit, with radiation from saidfirst source directed to said first resistor; a first RC delay circuitfor said first current control unit for increasing current through saidcurrent control unit to said first radiation source; a voltage source;and means for connecting said voltage source across said first delaycircuit for charging the capacitance thereof, with the current to saidfirst radiation source increasing as said capacitance charges toincrease the on time of said thyristor.
 2. A circuit as defined in claim1 wherein said current control unit includes a transistor with emitterand collector in series with said first radiation source, with saidfirst delay circuit connected to the transistor base for controllingcurrent in said first radiation source.
 3. A circuit as defined in claim1 whereiN said thyristor is a triac.
 4. A circuit as defined in claim 1wherein said controlled rectifier comprises two thyristors connected inparallel.
 5. A circuit as defined in claim 1 for operation with a threephase system and including three of said thyristors and switching units,with radiation from said first radiation source directed to the firstresistors of each of the three switching unit networks.
 6. A circuit asdefined in claim 5 including a closed container, with the firstresistors of each of the three phase shift networks mounted in the wallsof said container, and with said first radiation source mounted withinsaid container spaced substantially equally from each of the firstresistors.
 7. A circuit as defined in claim 6 wherein said container hasa square cross section with four faces, with said first resistorsmounted in three of said faces.
 8. A circuit as defined in claim 1including: a second resistor in said phase shift network and having aresistance varying as a function of received radiation; a secondradiation source connected in circuit with a second current controlunit, with radiation from said second source directed to said secondresistor; a second RC delay circuit for said second current control unitfor increasing current through said unit to said second radiationsource; and means for connecting said voltage source across said seconddelay circuit for charging the capacitance thereof, with the current tosaid second radiation source increasing as said capacitance charges toincrease the on time of said thyristor.
 9. A circuit as defined in claim8 with said phase shift network connected across said thyristor and withsaid first and second resistors connected in parallel.
 10. A circuit asdefined in claim 8 including means connecting said second currentcontrol unit to said first delay circuit.
 11. A circuit as defined inclaim 10 wherein said second current control unit and radiation sourceand said second phase shift network including said second resistor areselected such that fully charging the capacitance of said second delaycircuit turns said thyristor on only for a portion of the available ontime.
 12. A circuit as defined in claim 8 wherein said second currentcontrol unit and radiation source and said second phase shift networkincluding said second resistor are selected such that fully charging thecapacitance of said second delay circuit turns said thyristor on at apredetermined and adjustable phase angle of each half cycle.